Preheat the oven to 400 degrees F.
Spread the chopped potatoes onto a large baking sheet. Drizzle 2 tablespoons of olive oil over the potatoes, and sprinkle with the salt. Toss everything around to ensure the potatoes are evenly coated.
Bake the potatoes in the oven for 40-45 minutes, or until they’re tender.
Meanwhile, as the potatoes are baking, cook the spinach according to package directions using the microwave or stovetop.
When the spinach is done, pour it in a large bowl. Add the tuna, cherry tomatoes, and red onions to the bowl.
When the potatoes are done, add the warm potatoes to the bowl with the other ingredients.
Now, prepare the dressing: In a small bowl, whisk together the olive oil, mustard, honey, and vinegar. Pour the dressing into the large bowl with the other ingredients, and toss everything together so it’s evenly coated. Serve and enjoy!